Device and method for measuring parameters of logs of web material

ABSTRACT

The device ( 9 ) includes a feed path (P) of the logs (R), configured to feed the logs in a direction orthogonal to the axis of the logs; and one or more pick-up members ( 27 ) spaced from one another in a direction transverse to the feed path (P) of the logs (R). The pick-up members are adapted to pick up individual logs (R) from a pick-up position along the feed path (P); and transfer each log (R) from the measuring position back to the feed path substantially in the position in which it was picked up.

TECHNICAL FIELD

The present invention relates to improvements to devices and methods formeasuring one or more characteristic, i.e., parameters or sizes of a logof web material, for example but not exclusively logs of tissue paper,useful for controlling the production process.

BACKGROUND ART

In many industrial fields in which logs of wound web material areproduced, it is necessary to measure one or more parameters, i.e.,physical features of the logs, in order to take action on productionparameters to maintain the physical characteristics, i.e., theparameters of the logs produced within a predetermined range.

Typically, among the parameters, i.e., the physical characteristics ofthe logs, weight is important in the field of tissue paper, used toproduce rolls of toilet tissue, kitchen towels and similar articles. Afurther parameter, i.e., characteristic, which in some cases is usefulfor controlling the production process is firmness. The diameter of thelogs can also be important for controlling production.

Typically, the measurements of at least some of these parameters takesplace in a laboratory, on samples of logs picked up from the productionline. This measuring method is not satisfactory, as the measurementobtained outside the line does not allow real time correction of theproduction parameters in order to correct any divergences of thefirmness measured relative to the values desired.

A device and a method to overcome this drawback are disclosed inEP1530044. In the measuring system disclosed therein each log producedis fed along a feed path with a movement parallel to the axis of thelog. Located along the feed path is a device for firmness measuring,provided with a wheel positioned at a distance with respect to a surfaceon which the log is supported, so as to apply a known compressive forceto the log, when the log passes between the wheel and the supportingsurface. The thrust exerted by the log on the wheel causes lifting ofthe wheel. The displacement of the wheel is a function of the diameterof the log and of the compressive deformation (compression) of the logcaused by the force applied by the wheel.

This system is particularly complex and requires the logs to be fed inthe direction of their axis. This condition is incompatible with theconfiguration of the majority of production lines for logs of tissuepaper, where the logs produced by a rewinder are fed along the feed pathby rolling and hence orthogonally to their axis.

Moreover, the measuring system disclosed in EP1530044 is notparticularly precise. In fact, due to the configuration of the measuringsystem, any compression deformations of the tubular winding core onwhich the log is formed are erroneously added to the compression of thewound material. The more deformable the tubular winding core, thegreater this measurement defect will be. In an effort to reduceconsumables, increasingly thin winding cores are produced, making themincreasingly deformable by compression and tending to make the firmnessmeasurement imprecise.

To solve some of the defects of the device described in EP1530044, morereliable systems for measuring the firmness of the logs have beendeveloped and are disclosed in WO2019185438. The systems and the methodsdisclosed herein are much more efficient and precise than those of theprior art and overcome many of the intrinsic limits. Nonetheless, thereis still room for further improvements, in particular in order to obtainmore precise measurements and simpler measurement devices.

SUMMARY OF THE INVENTION

According to an aspect, disclosed herein is a device for measuringparameters of a log of wound web material, including a feed path for thelogs, configured to feed the logs in a direction orthogonal to the axisof the logs, and one or more pick-up members, for example two pick-upmembers spaced from one another in a direction transverse to the feedpath of the logs. The pick-up member or members is/are adapted to pickup individual logs from a pick-up position along the feed path and totransfer each log from the measuring position back to the feed path.

The number of pick-up members can depend on the length of the logs to behandled. For short logs, i.e., with a limited longitudinal dimension, asingle pick-up member may suffice. For longer logs, a pair of pick-upmembers may be required, or even more than two pick-up members alignedwith one another in a direction transverse to the direction of movementof the logs along the feed path.

The device can be controlled to randomly pick up logs, and to measureone or more parameters of these logs. In some embodiments, the devicecan be configured to measure only the weight of the log. In otherembodiments the device can be configured to measure only the firmness ofthe log.

In particularly advantageous embodiments, the device can be configuredto measure both the firmness and the weight of the log.

To obtain further useful information, the device can also measure thediameter of the log, or can be combined with a different device thatmeasures the diameter of the log, even in a position distanced from thepoint in which the device is located.

In embodiments described herein, the device has many advantages withrespect to known devices, including its simplicity and limitedfootprint, while maintaining high measurement precision and flexibility.

The device thus configured can be inserted in existing converting lines,i.e., lines for producing logs from reels of large diameter, forinstance, substantially without requiring to modify the layout thereof,or with minor modifications. This is facilitated by the small footprintof the device, which can be inserted into existing spaces along apreviously installed line.

In advantageous embodiments, the pick-up member(s) is(are) adapted tomeasure at least one parameter of the picked-up log, while the log isengaged with the pick-up member(s). In particular, each pick-up membercan comprise a respective weight sensor, for example a load cell, whichallows the weight of the log picked up by the pick-up members to bemeasured, while the log is still engaged with said pick-up member(s).This allows fast measurements to be obtained with a very compactstructure of the device.

Advantageously, the pick-up member(s) is(are) adapted to transfer eachlog picked up from the measuring position back to the pick-up positionalong the feed path of the logs. In other terms, the logs are picked upfrom the feed path in one point and re-inserted into the feed path inthe same point in which they were picked up. This contributes to thesimplicity and compactness of the device.

In advantageous embodiments, each pick-up member comprises a gripperwith a first jaw and a second jaw, the first jaw being located upstreamof the second jaw with respect to the direction of feed of the logsalong the feed path. In embodiments disclosed herein, the first jaw andthe second jaw pivot about respective pivot axes orthogonal to thedirection of feed of the logs along the feed path and parallel to theaxes of the logs and their movement can advantageously be controlled bya first actuator for controlling the movement of the first jaw and by asecond actuator for controlling the movement of the second jaw. Thefirst and the second actuator can be independent and controlled in amanner coordinated with respect to each other, to perform suitablemaneuvers with the jaws of the grippers.

As will be described below, with reference to an exemplary embodiment,this allows operations to pick up and release the individual logs in theflow of the logs along the feed path, without interfering with orobstructing the normal feed of the logs.

Feed of the logs along the path can take place by rolling under theeffect of gravity, the path being defined by an inclined chute, forinstance.

In particularly simple embodiments, the device can comprise only one ormore pick-up members, with which sensors, for example load cells formeasuring weight, are associated.

However, in more complex and complete embodiments, the measuring devicecan have a measuring system of the log firmness. This system cancomprise a pair of blocking heads, adapted to block a log by means oftailstocks, located above the feed path and at the sides of the feedpath. At least one of the blocking heads, and preferably each blockinghead, comprises a log firmness measuring member. In embodiments, theblocking heads are aligned transverse to the feed path along a directionorthogonal to the direction of feed of the logs along the feed path andparallel to the direction of the axes of the logs along the feed path.The pick-up member(s) is(are) adapted to position each picked-up log ina measuring position, in which the log interacts with the blocking headsand with the log firmness measuring member, associated with the blockinghead.

Each log firmness measuring member can, for example, comprise a presseradapted to apply a predetermined load against the surface of a logpicked up from the feed path and a measuring arrangement of the degreeof penetration of the presser in the log as a result of a predeterminedload applied by the presser.

Further advantageous features and embodiments of the device are definedin the appended claims, which form an integral part of the presentdescription.

According to a further aspect, described herein is a method formanufacturing logs of web material, comprising the following steps:

-   -   sequentially producing logs of web material;    -   feeding the logs of web material in a feed path, in which the        logs of web material are fed in a direction orthogonal to the        axis of the logs;    -   by means of one or more di pick-up members spaced from one        another in a direction transverse to the feed path of the logs,        picking up a log from a pick-up position along a feed path of        the logs;    -   measuring at least one parameter of the picked-up log;    -   returning, by means of the pick-up member(s), the log in the        feed path.

Further advantageous embodiments of the method are described below anddefined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by following the description andthe accompanying drawings, which illustrate a non-limiting exemplaryembodiment of the invention. More in particular, in the drawings:

FIG. 1 shows a schematic side view of a portion of a production line oflogs of tissue paper;

FIG. 2 shows an axonometric view of the measuring device;

FIG. 3 shows a front view of the device of FIG. 2;

FIG. 4 shows a section according to IV-IV of FIG. 3;

FIG. 5 shows an axonometric view of one of the two blocking heads;

FIG. 6 shows an axonometric view of one of the pick-up members of thelogs;

FIG. 7 shows a front and partially sectional view on a vertical plane ofthe pick-up member of FIG. 6;

FIGS. 8A to 8J show a sequence of picking up a log from the feed pathand repositioning the log in the feed path after measurement;

FIGS. 9A-9E show a sequence of measuring the log firmness.

DETAILED DESCRIPTION

FIG. 1 schematically shows a side view of a portion of a converting line1 for producing logs R of tissue paper. The converting line 1 comprisesa rewinder 7, that winds one or more plies of tissue paper V1, V2 comingfrom an unwinder 3 and unloads them into a feed path P that passesthrough a tail sealer 8. The tail or outer edge of the wound webmaterial in each log R is sealed to the outer surface of the log by thetail sealer 8. Arranged downstream of the tail sealer 8 is a measuringstation, located in which is a measuring device 9 that measures one ormore parameters of logs R picked up randomly from the feed path P of thelogs along the converting line 1. Arranged downstream of the measuringstation, there can be one or more further stations of the convertingline, for example a storage unit 11 and a log saw 12 that cuts each loginto rolls of smaller axial dimensions, which are then packaged in apackaging section (not shown) of the converting line 1.

The measuring device 9 and its operating cycle will be described indetail hereunder, with specific reference to FIGS. 2 to 9. The letter Pindicates the feed path of the logs R, which in the device 9 is definedby a chute 21 or other surface for supporting the logs. In theillustrated embodiment, the feed path P is configured so as to allowfeed by gravity; the logs R roll on the chute 21, which is inclined tofacilitate feed of the logs R. Nonetheless, it would also be possible toprovide a feed path in which the logs R are controlled and moved by feedmembers.

The measuring device 9 comprises a stationary bearing structure, whichhas a cross member 25 extending transverse to the feed path P, and hencetransverse to the direction of feed of the logs R along the feed path P,represented by the arrow P.

One or more pick-up members 27 are mounted on the cross member 25. Inthe illustrated embodiment two pick-up members 27 are provided.

In the illustrated embodiment, the pick-up members 27 are substantiallythe same as one another. In other embodiments, the pick-up members 27can be symmetrical with respect to a vertical plane, parallel to thefeed path P of the logs R.

The pick-up members 27 are spaced from one another along the crossmember 25, so as to engage the logs R, on which the measurements arecarried out. In the illustrated embodiment, the pick-up members 27 arelocated in two positions fixed with respect to the transverse direction(orthogonal to P), but it would also be possible to mount the pick-upmembers 27 so that their mutual distance and/or their position withrespect to the direction transverse to the feed path P is adjustable,for example as a function of the axial length of the logs R.

The measuring device 9 further comprises two blocking heads 29,substantially symmetrical to each other with respect to a planeorthogonal to the cross member 25 and located on opposite sides of thefeed path P. The two blocking heads 29 are located externally to thepick-up members 27 and are movable according to the double arrows f29parallel to the cross member 25 to move toward and away from each other.

The structure and the function of the pick-up members 27 is described indetail below with reference in particular to FIGS. 2, 3, 4, 6 and 7.

Each pick-up member 27 is movable along a respective vertical upright31, integral with the cross member 25. A load-bearing structurecomprising a slide 33 of the pick-up member 27 slides along the upright31 according to the double arrow f33. In FIGS. 2 and 3 the two pick-upmembers 27 are shown in their lowest position.

The lifting and lowering movement according to f33 of the slides 33 iscontrolled by respective linear actuators 35, for examplepiston-cylinder actuators.

A gripper 37, comprising a first jaw 37A and a second jaw 37B, isconstrained to each slide 33. The two jaws 37A, 37B are different fromeach other. More precisely, the first jaw 37A, which is located upstreamof the second jaw 37B with respect to the direction of feed of the logsR along the feed path P, is shorter than the second jaw 37B. In theillustrated embodiment, the second jaw 37B comprises, by way of example,a concave surface 37C against which the log R is pushed by the first jaw37A, as will be described in greater detail below with reference to anoperating cycle.

Each of the two jaws 37A, 37B is controlled by its own actuator. A firstactuator 39A controls the first jaw 37A and a second actuator 39Bcontrols the second jaw 37B. The actuators 39A, 39B can beelectronically controlled electric motors or other rotary actuators,which move the two jaws 37A, 37B about rotation axes A parallel to eachother and parallel to the cross member 25. The use of two separateactuators 39A, 39B for the two jaws 37A, 37B of each gripper 37 allowsthe two jaws 37A, 37B to caiiy out rotation movements about the axes Athat are staggered from each other, for reasons that will be apparentfrom the description of an operating cycle. Therefore, the actuators areindependent but controlled so as to carry out coordinated movements withrespect to each other.

The jaws 37A. 37B and the actuators 39A, 39B are supported by the slide33 by means of a support 40, which is constrained to the slide 33 withthe interposition of a load cell 41. In this way, the load cell 41 ofeach gripper 37 can measure the weight of a log R engaged by thegrippers 37 in the manner described hereunder.

Each blocking head 29 has a structure described below with reference inparticular to FIGS. 2, 3 and 5. Each blocking head 29 comprises anupright 50 engaged with guides integral with the cross member 25, notshown, to move according to the double arrow f29 parallel to the crossmember 25. The movement according to f29 is imparted to each measuringhead 29 by an actuator, not shown, for example an electronicallycontrolled electric motor.

With reference in particular to FIG. 5, a tailstock 61, orientedparallel to the cross member 25, is fixed in the lower part of theupright 50 of each blocking head 29. The two tailstocks 61 of the twoblocking heads 29 are oriented facing each other and are coaxial.

An arm 63, which carries log firmness measuring members, indicated as awhole with 65, can be fixed on the upright 50 of the blocking head 29,above the respective tailstock 61. The firmness measuring members 65comprise a presser 67 integral with a rod 67A integral with a slide 69,which slides in vertical direction according to the double arrow f69along a guide 71 integral with the arm 63. In other embodiments, themeasuring member 65 can be provided on only one of the two blockingheads 29.

A linear actuator 73, for example a piston-cylinder actuator, isconnected to the slide 69 and controls the movement thereof according tothe double arrow f69. A bracket 77 constrains the rod of the linearactuator 73 to the slide 69. A measuring arrangement, i.e., a sensor 75,for example a laser sensor, measures the position of the slide 69 andhence of the presser 67 with respect to the arm 63 and with respect tothe tailstock 61.

The presser 67 is calibrated in diameter and weight and applies a knowncompression force on the log R that is positioned in the measuringdevice. By means of the laser sensor 75, or other suitable sensor, thedegree of penetration of the presser 67 into the wound web material ofthe log R is determined in order to detect the firmness, as described ingreater detail below.

In addition to the members described herein, a measuring system of thediameter of the logs R is also associated with the measuring device 9.Purely by way of example, in FIG. 2 this measuring system is representedas a laser emitter 81, which detects the passage of the logs anddetermines the diameter thereof. In some embodiments, the measuringsystem 81 is positioned so as to measure the diameter of a log R whenthis is close to the grippers 37 of the pick-up members 27.

In brief, the measuring cycle is as follows. Measurements are carriedout randomly only on some logs R being fed along the feed path P throughthe measuring device 9. The logs can be chosen randomly, either by anoperator, or in a programmed manner, for example one log every N logsproduced, or in any other suitable way. Operation of the measuringdevice 9 is controlled by means of a control unit indicatedschematically with 100 in FIG. 2 and that can be interfaced with ahigher-level control unit, which manages the converting line 1. Thecontrol unit 100 can advantageously be interfaced with the sensors andthe actuators described above, in particular with the actuators 39A 39B,35, 73 and with the sensors 41, 75, 81.

The sequence of FIGS. 8A-8J illustrates in detail the operation of apick-up member 27. In FIG. 8A the pick-up member 27 is in an idleposition and is above the feed path P of the logs R, which can passthrough the measuring device 9 without interacting therewith.

FIGS. 8B-8J show the pick-up sequence of a single log R from the feedpath P, the transfer thereof to the blocking heads 29 and the releasethereof into the feed path P (FIG. 8G), substantially in the sameposition from which it was picked up (FIG. 8B).

To pick up a log R, the pick-up members 27 are lowered toward the chute21 to a height such as to interact with the logs R. The second jaw 37Bof the gripper 37 is rotated downward (FIG. 8B), in order to stop theapproaching log R. Once the approaching log R is in contact with thesecond jaw 37B, condition that can be detected, for example, by aphotocell, not shown, the first jaw 37A of the gripper 37 is lowered,closing the gripper 37 and engaging the log R in the gripper.

After the log R has been gripped, the pick-up members 27 are lifted(FIG. 8D) to take the log R out of the feed path of the logs P. More inparticular, the log R is taken with its tubular winding core C inalignment with the tailstocks 61 of the blocking assembly 29, so thatthese, by moving toward each other (arrow f29), are inserted fromopposite ends in the tubular winding core C. When the tailstocks 61 haveengaged the log R, the grippers 37 open (FIG. 8E) and release the logRon the tailstocks, so that the firmness of the log is measured, in themanner described below with reference to the sequence of FIGS. 9A-9E.After the firmness measurement has taken place, the grippers 37 closeagain (FIG. 8F), the tailstocks 61 are extracted from the tubular core Cand the grippers 37 are lowered to release the log R on the chute 21 inthe feed path P. The log R continues rolling along the path, while thepick-up members 27 are lifted again (FIG. 8H) and the jaws 37A, 37B open(FIG. 8I) and finally the pick-up members 27 with the open grippers movetoward the chute 21 (FIG. 8J) in the position in which a new log R canbe picked up, repeating the above described sequence.

In practice, the logs R are picked up randomly, with a frequency thatcan be fixed or variable, automatically and/or manually controlled, soas to repeat with the most suitable frequency a random control on theparameters (diameter, weight and compactness) of the logs produced bythe rewinder.

During the steps described above, and preferably before the step of FIG.8E, the weight of the log R is measured by means of the load cells.

The sequence of FIGS. 9A-9H illustrates the operations carried outduring the measuring cycle by the blocking heads 29 and by the measuringassembly 65. The operations illustrated in the sequence of FIGS. 9A-9Hare coordinated with the operations carried out by the pick-up members27 illustrated in FIGS. 8A-8J.

In FIG. 9A the pick-up members 27 have carried the log R in alignmentwith the tailstocks 61. By means of a laser sensor or other suitablemeans, such as a video camera, the position of the log R for correctinsertion of the tailstocks 61 is detected. Centering between thetubular core C of the log R and the tailstocks 61 can take place with alifting and lowering movement of the grippers 37 and with a synchronizedrotation movement of the jaws 37A, 37B of each gripper 37 that causes amovement with a horizontal component of the log R. For embodiments withtwo or more grippers 37, these can be controlled separately from oneanother, so as to be able to center the two ends of the tubular windingcore C relative to the two tailstocks 61.

Once the tailstocks 61 and the tubular winding core C have been aligned,the two blocking heads 29 can be moved toward each other so as to insertthe tailstocks 61 in the tubular core C, see FIG. 9B. In this step, thelog R is still engaged by the jaws 37A, 37B of the grippers 37.

In the subsequent step (FIG. 9C), the jaws 37A, 37B of the grippers 37open and the log R is placed on the tailstocks 61, which come intocontact with the inner surface of the tubular core C. In this positionthe log firmness can be measured. To this end, the linear actuator 73lowers the presser 67. The actuator 73 comprises a rod 73A that engagesin a hole of a plate 69A of the slide 69 (FIG. 9D), so that the actuator73 can extend completely, while the presser 67 comes into contact withthe outer surface of the log R and stops at a height that is determinedby the extent to which the wound web material in the log R is compressedunder the weight of the presser 67 alone. FIG. 9E schematically showshow the presser 67 penetrates the theoretical cylindrical surface of thelog R compressing the turns of wound web material. The penetration depthis proportional to softness, and hence is a function of the firmness ofthe log R.

The sensor 75 detects the position of the log R with respect to theposition of the presser 67. When the presser 67 reaches the surface ofthe log (FIG. 9D) the sensor detects the degree of penetration P1 of thepresser 67 based on the diameter of the log R, which was measured orwill be measured by the sensor 81.

The compression measured is determined solely from the variation ofthickness of the material comprised between the presser 67 and thetailstock 61. Therefore, the firmness measurement obtained is notaffected by errors, typical of prior art measuring systems, due tocompression of the tubular winding core during measurement.

The random measurement of the firmness of the log R can be used to takeaction on the production parameters of the converting line. Typically,the firmness of the log can be corrected, if the measurement is outsidean admissible range, by acting on the tension of the web material in therewinder and/or by acting on the embossing conditions of the pliesforming the web material of the log, in a manner known per se by thoseskilled in the art.

What is claimed is:
 1. A device for measuring parameters of a log ofwound web material, comprising: a feed path of the logs, configured tofeed the logs in a direction orthogonal to the axis of the logs; atleast one pick-up member adapted to: pick up individual logs from apick-up position along the feed path; and transfer each log from themeasuring position back to the feed path.
 2. The device of claim 1,comprising two pick-up members spaced from one another in a directiontransverse to the feed path of the logs.
 3. The device of claim 1,wherein said at least one pick-up member is adapted to measure at leastone parameter of the picked-up log, while the log is engaged with thepick-up members.
 4. The device of claim 1, wherein said at least onepick-up member is adapted to transfer each log picked up from themeasuring position back to the pick-up position along the feed path ofthe logs, each pick-up member comprising a lifting and loweringactuator, adapted to transfer the pick-up member from the pick-upposition to the measuring position and vice versa.
 5. The device ofclaim 1, wherein each pick-up member comprises a log weight measuringmember.
 6. The device of claim 1, wherein each pick-up member comprisesa gripper with a first jaw and a second jaw, the first jaw being locatedupstream of the second jaw with respect to the direction of feed of thelogs along the feed path; and wherein the first jaw and the second jawpivot about respective pivot axes orthogonal to the direction of feed ofthe logs along the feed path and parallel to the axes of the logs in thefeed path.
 7. The device of claim 6, wherein each gripper comprises afirst actuator for controlling the movement of the first jaw and asecond actuator for controlling the movement of the second jaw.
 8. Thedevice of claim 6, wherein the second jaw is longer than the first jaw.9. The device of claim 5, wherein each pick-up member comprises agripper with a first jaw and a second jaw, the first jaw being locatedupstream of the second jaw with respect to the direction of feed of thelogs along the feed path; wherein the first jaw and the second jaw pivotabout respective pivot axes orthogonal to the direction of feed of thelogs along the feed path and parallel to the axes of the logs in thefeed path; and wherein each log weight measuring member comprises a loadcell, and wherein the load cell is located between a support, on whichthe respective gripper is mounted, and a bearing structure, movablerelative to the feed path of the logs to transfer the gripper from thepick-up position to the measuring position, and vice versa.
 10. Thedevice of claim 1, comprising a pair of blocking heads, located abovethe feed path and at the sides of the feed path; wherein at least one ofthe blocking heads comprises a log firmness measuring member; whereinthe blocking heads are aligned transverse to the feed path along adirection orthogonal to the direction of feed of the logs along the feedpath and parallel to the direction of the axes of the logs in the feedpath; and wherein the pick-up member or members is/are adapted toposition each picked-up log in a measuring position, in which the loginteracts with the blocking heads.
 11. The device of claim 10, whereineach blocking head comprises a respective log firmness measuring member.12. The device of claim 10, wherein each log firmness measuring membercomprises a presser adapted to apply a predetermined load against thesurface of a log picked up from the feed path and a measuringarrangement of the degree of penetration of the presser into the log asa result of the predetermined load applied by the presser.
 13. Thedevice of claim 10, wherein: each blocking head is movable in adirection orthogonal to the direction of feed of the logs along the feedpath and parallel to the axes of the logs; and wherein each blockinghead comprises a tailstock adapted to be inserted into a tubular windingcore of the logs; the tailstocks of the two blocking heads are alignedwith and symmetrical to each other; and the movement of the blockingheads is controlled so as to insert the two tailstocks in opposite endsof the winding core of a log in the measuring position and extract themfrom said ends.
 14. The device of claim 10, wherein each blocking headis movable in a direction orthogonal to the direction of feed of thelogs along the feed path and parallel to the axes of the logs; whereineach blocking head comprises a tailstock adapted to be inserted into atubular winding core of the logs; the tailstocks of the two blockingheads are aligned with and symmetrical to each other; wherein themovement of the blocking heads is controlled so as to insert the twotailstocks in opposite ends of the winding core of a log in themeasuring position and extract them from said ends; and wherein thepresser is adapted to coact with the respective tailstock to apply aforce orthogonal to the tailstock and cause compression of the materialof the log comprised between the presser and the tailstock.
 15. Thedevice of claim 13, wherein each blocking head comprises a centeringsystem between the tailstock and the winding core of the log picked upfrom the feed path.
 16. The device of claim 15, wherein the centeringsystem is interfaced with a control unit that, based on signals of thecentering system, moves each pick-up member relative to the tailstocks.17. The device of claim 1, comprising a log diameter measuring system.18. A method for manufacturing logs of web material, comprising thefollowing steps: sequentially producing logs of web material; feedingthe logs of web material in a feed path, in which the logs of webmaterial are fed in a direction orthogonal to the axis of the logs; byat least one pick-up member, picking up a log from a pick-up positionalong the feed path of the logs; measuring at least one parameter of thelog picked up; returning, by said at least one pick-up member, the logto the feed path.
 19. The method of claim 18, wherein the step ofpicking up the log is carried out by two pick-up members spaced fromeach other in a direction transverse to the feed path of the logs. 20.The method of claim 18, wherein the step of measuring at least oneparameter of the picked-up log is carried out while the log is engagedwith the pick-up member or members.
 21. The method of claim 20, whereinthe step of measuring at least one parameter of the picked-up log whenthe log is engaged with the pick-up member or members comprises the stepof measuring the weight of the log by means of sensors positioned on thepick-up member or members.
 22. The method of claim 18, wherein thepick-up member or members return the log to the pick-up position alongthe feed path.
 23. The method of claim 18, further comprising thefollowing steps: by the pick-up member or members, transferring the logpicked up from the feed path to a measuring position, in which oppositeends of the log interact with a pair of blocking heads, arranged abovethe feed path and at the sides thereof; wherein the blocking heads arealigned in a direction transverse to the direction of feed and parallelto the axis of the logs along the feed path; by a measuring system, andpreferably by two measuring systems, installed respectively on one orboth blocking heads, measuring the log firmness.
 24. The method of claim18, further comprising the following steps: in the measuring position,inserting into each end of a tubular winding core of the log, arespective tailstock of the respective blocking head and releasing thelog from the pick-up member or members; by means of a presser, applyinga force on the outer surface of the log, approximately orthogonally toat least one of said tailstocks while the log is supported by thetailstocks; measuring the degree of compression of the material of whichthe log is formed between the presser and the tailstock.
 25. The methodof claim 18, further comprising the step of measuring the diameter ofthe log, preferably before it is picked up by the pick-up member ormembers
 26. The method of claim 18, comprising the step of modifying atleast one log production parameter as a function of at least one,preferably two, and more preferably three, of the following parametersof the log: log weight, log diameter, log firmness.